1. Field of the Invention
The present invention provides novel hydrophobically associating terpolymer compositions containing cationic functionality. These water soluble or water dispersible polymers contain both water soluble and water insoluble monomers. The water soluble monomers are ethylenically unsaturated nonionic monomers, such as acrylamide (AM), and a salt of an ethylenically unsaturated amine base (C), such s 3-methacrylamidepropyltrimethylammonium chloride (MAPTAC), 2-methacrylatoethyltrimethylammoniuim chloride (METAC) and diallyl dimethylammonium chloride (DMDAAC). The hydrophobic or water insoluble monomer is a higher alkyl(meth)acrylamide or alkyl(meth)acrylate (R). These polymers are hereinafter referred to as CRAM. While the novel compositions of this invention impart unusal properties to water based fluids, they are extremely efficient for clean-up of waste waters containing organic contaminants and for breaking oil-in-water emulsions.
2. Description of the Prior Art
The production of waste water clean enough for safe disposal continues to be a problem, especially when oil is emulsified in the primary waste water. In oil production, especially where high levels of water flooding or steam flooding are being practiced, oil-in-water emulsions are generated. These water continuous emulsions are generally referred to as reverse emulsions since the more usual oil field produced fluid is a water-in-oil emulsion. Reverse emulsions are difficult to break and generally result in large volumes of oil contaminated waste water that must be treated for removal of oil and solids before disposal by either release to surface streams, injection or use as boiler water make-up for steam generation. Other oil-in-water emulsions of concern in the waste water treating area are those produced as a result of steel mill and metal working operations, food processing, refinery and chemical plant operation, cooling water blow-down, bitumen extration from tar sands and shale oil operations, rain water run-off and a host of others. These emulsions all have in common the fact that the oil or organic phase is insoluble in the water contnuous phase. The amount of oil dispersed in these water continuous emulsions varies from a few to several hundred parts per million in waste waters to several percent (5% to 25%) in fluids right out of the wellhead.
The oil is generally well dispersed in the water phase as very small droplets that are stabilized as a result of the presence of natural surfactants. The stability of these oil-in-water emulsions generally results from either a negative charge imparted to the droplets by these surfactants; from steric stabilization caused by surfactants; by the shear which the fluid experiences during production, which causes the generation of smaller and more stable droplets; or from several other sources. As the density of the organic phase becomes higher, approaching that of the water phase, further stability is imparted to the emulsion. The presence of fine solids, such as clays, sands, corrosion products, etc., in the fluids add to the stability of these oil-in-water emulsions. The stability of these oil-in-water emulsions must be overcome if the oil is to be removed from the water before disposal or in order to separate the oil from the water in the produced fluids in the case of oil production in water floods and steam floods.
Current practice is to attempt to break waste water oil-in-water emulsions using various mechanical techniques, such as API separators, induced air flotation (IAF), dissolved air flotation (DAF) or other methods. In the API separator method time is allowed for the oil droplets to come together and float to the surface or to settle to the bottom, if it is adsorbed on solids. In many cases just a large tank is used to provide a long holding time for a fluid under essentially low flow or quiescent conditions. The expectation is that the long residence time will permit coalescence and settling of the oil droplets. In the flotation methods air or another gas, such as natural gas or produced gases in the oil field where the waste water is generated, is used to form very small gas bubbles under the surface of the waste water which float to the surface. As the gas bubbles rise to the surface the oil droplets attach themselves and rise to the surface with them, concentrating at the surface where the oil can be removed.
Various chemicals, surfactants and polymers are generally applied to these waters to enhance the separation of oil and water using the above methods and, in some cases, are required if the method is to work at all. These chemicals are used to aid in foam generation in flotation. In addition, they may be used to cause oil droplet surface charge neutralization, which results in destabilization of the oil-in-water emulsion. This destabilization results in agglomeration of the oil droplets, floc formation, and possibly several other beneficial effects. While the use of such chemicals generally enhances the separation of oil from oil-in-water emulsions, there remains significant room for improvement.
Typically, treatment polymers are mixed into the waste water using various levels of shear. The water is then allowed to stand in a quiescent state for several hours or days until the oil flocculates and floats to the surface, where is it skimmed off. The water phase containing any residual oil is removed from beneath the surface and is either further treated, reused or is disposed of. As an alternative, to the above quiescent aging method, the polymer treated water can be sent to a gas flotation device for oil removal as described above.
Reverse emulsions produced at the wellhead in steam floods or water floods are generally treated with surfactants and polymers in a similar way. However, flotation equipment is not generally used on the wellhead fluid, but is used on the water, which we have called waste water, broken out of the produced emulsion. A more typical practice would be the use of settling tanks which hold the produced fluid in a quiescent state at elevated temperature for a period of time. This equipment may vary from a simple tank to devices which add heat and make use of electrical fields to accelerate the breaking of emulsions.
Improved methods for resolving oil-in-water emulsions, such as those produced at the wellhead, would find significant utility and environmental benefit. For example, if the level of residual oil remaining in the treated water could be reduced, or the speed of oil removal increased then a more economical treating operation would result. These improvements in treating method would provide both an economic and environmental benefit. The present invention describes an improved process for treating oil-in-water emulsions.
The type of water soluble polymers currently used are generally acrylamide copolymers or melamine/formaldehyde polymers or others. For example, Bolhofner in U.S. Pat. No. 4,472,284 describes the treatment of water containing fats, oils and greases using a melamine-formaldehyde condensation product, alone or in combination with a polyacrylamide. Rather high polymer concentrations are needed and a two polymer system can present handling difficulties during field operations.
Another approach to the treatment of waste water involves the use of water insoluble polymeric adsorbents as described by Renner in U.S. Pat. Nos. 3,716,483 or Takegani, et al. in 4,081,403. These processes for treating waste water are costly and cannot achieve the degree of clean-up of the present invention.
Another approach involves the use of copolymers of acrylamide with various cationic monomers of various comonomer ratios. Some of the cationic monomers that have been used are: methacrylamidoalkyltrimethylammonium salts, such as 3-methacrylamidopropyl trimethylammonium chloride (MAPTAC), as described in U.S. Pat. No. 4,160,742, or similar acrylate esters; diallyl dialkyl ammonium salts, as described by Booth and Linke in U.S. Pat. Nos. 3,147,218 and in 3,316,181; salts of dimethylaminoethylmethacrylate and the like. Buris, et al., U.S. Pat. No. 4,224,150, describe a process for clarifying aqueous systems employing quaternary ammonium adducts of polymerizable tertiary ammonium salts and acrylamide. These polymers are generally available as high molecular weight materials, either in aqueous solution, as emulsions of various types, or in solid form, which requires dissolution before use. The efficiency of resolving oily water or demulsifying oil-in-water emulsions, as well as the degree of final clean-up, are two areas where further improvement in treatment performance would be highly desirable. One of the objects of this invention is to decribe a class of novel terpolymers which provide this improvement.
The use of hydrophobic groups on water soluble polymers to enhance the rheological properties of water based fluids has been described. One approach to provide polyacrylamide based systems containing hydrophobic groups is described by Bock, et al., U.S. Pat. No. 4,520,182. Water soluble acrylamide copolymers containing a small amount of oil soluble or hydrophobic alkylacrylamide groups were found to impart efficient viscosification to aqueous fluids. Landoll, U.S. Pat. No. 4,304,902, describes copolymers of ethylene oxide with long chain epoxides which also required relatively large polymer concentration (approximately 1%) for thickening water and required surfactants for solubility due to irregularities in the polymerization. In a related case, U.S. Pat. No. 4,428,277, modified nonionic cellulose ether polymers are described. Although these polymers show enhanced viscosification relative to polymers not containing hydrophobic groups, the viscosification efficiency was very low, requiring 2 to 3 weight percent polymer to provide an enhancement. The use of surfactants to enable solubility and, in turn, viscosification, by a water soluble polymer containing hydrophobic groups is described by Evani, U.S. Pat. No. 4,432,881. The hydrophobic groups claimed are attached to the polymer via an acrylate linkage which is known to have poor hydrolytic stability. In addition, the need for a surfactant to achieve solubility and thickening efficiency should make such a system very salt sensitive, as well as very sensitive to small changes in surfactant and polymer concentrations. Emmons, et al., U.S. Pat. No. 4,395,524, teaches acrylamide copolymers as thickeners for aqueous systems. While these polymers possess hydrophobic groups they are prepared using alcohol containing solvent which are known chain transfer agents. The resulting polymers have rather low molecular weights and, thus, relatively high polymer concentrations are required to achieve reasonable viscosification of water based fluids. While these polymers containing hydrophobic groups are disclosed as providing aqueous thickening properties, their use for oil water clean-up or to break oil-in-water emulsions is not taught. Furthermore, the combination of hydrophobic groups and cationic groups in a water soluble polymer is not taught, nor the use of this combination for oily water treatment.
One of the objects of this invention is to overcome the deficiencies in the use of the water soluble polymers of the prior art for treating oily waste water and resolving oil-in-water emulsions. A new class of water soluble polymer will be described which can be used at a lower treat rate and, hence, is more efficient than prior art materials for oily water treatment. Furthermore, these novel terpolymers of the instant invention provide a superior degree of clean-up or oil removal in comparison to the prior art materials. These new polymers contain a nonionic water soluble monomer, such as acrylamide, a cationically charged water soluble ethylenically unsaturated amine based monomer, such as 3-methacrylamidopropyltrimethylammonium chloride (MAPTAC), and a water insoluble or hydrophobic monomer, such as an alkyl(meth)acrylamide or alkyl(meth)acrylate with a chain length of six carbons or greater.
When these polymers are placed in an aqueous solvent the hydrophobic groups aggregate or associate in a manner similar to a surfactant. This hydrophobic association between polymer chains in solution results in an increase in the hydrodynamic size of the molecule, which, in turn, causes an increase in viscosity. In addition, if oil droplets are present there is an attractive interaction between the hydrophobic groups and the hydrophobe oil droplets. We have found that the presence of cationic groups, such as 3-methacrylamidopropyltrimethylammoniuim chloride (MAPTAC) causes an expansion of the polymer in solution, an improvement in polymer solubility and a favorable interaction with the hydrophobic groups. Thus, polymers containing both cationic amine based groups and hydrophobic groups provide a significant improvement in viscosification efficiency of water based systems. The synergism between the cationic and hydrophobic groups in terms of oily water treatment or breaking of oil-in-water emulsions also sets these polymers apart from those of the prior art.
Synthesis of the hydrophobically associating polymers of the instant invention present difficulties. In order for polymerization to be effected the monomers must obviously come into close proximity to one another. The incompatibility of the oil soluble and water soluble monomers prevents an effective concentration of one or the other of these monomeric species from being achieved at the locus of polymerization of the other comonomer. Several processes described in the prior art could conceivably achieve this, but have serious deficiencies, necessitating the invention described more fully in copending application Attorney Docket No. C-1960. For example, simply dispersing the water insoluble monomer as fine particles in the aqueous medium containing dissolved water soluble monomers would result in low incorporation of the water insoluble monomer and would lead to a heterogeneous product of particles dispersed in a predominantly water soluble polymer. The resulting polymer could not be used to impart efficient and uniform thickening to water based fluids, nor be very effective in treating oily water.
Techniques for polymerizing the water soluble polymers, such as those taught in U.S. Pat. Nos. 4,154,190, 3,211,708, 3,002,960 and 3,284,393, cannot be used to prepare the compositions of this invention. Also, techniques or processes for preparing cationic polymers or copolymers containing cationic monomers, such as U.S. Pat. Nos. 4,452,957, 4,283,517, 4,160,742 and 3,316,181 have deficiencies in terms of incorporating the hydrophobic monomers needed for the polymers of this invention. This art does not teach the formation of a sufficiently fine dispersion of the water and oil soluble monomers to enable uniform reaction and homogeneous terpolymers to be produced. The use of mutual solvents or solvent mixtures to dissolve the water and oil soluble monomers as taught by Lenke, et al., U.S. Pat. No. 4,151,333, and Barua, et al., U.S. Pat. No. 4,098,987, has some serious limitations. Although this approach undoubtedly allows the incompatible monomers to come into close proximity to one another, since the dispersion is on a molecular scale, often the resulting copolymer is insoluble in the same solvent as shown in U.S. Pat. No. 4,151,333. This leads to precipitation of the copolymer before it has achieved sufficient molecular weight required in many applications, such as aqueous viscosification or oily water treatment. The use of water miscible solvents, such as alcohols, ether and actone, either along or with water, as taught in U.S. Pat. No. 4,098,987, results in low molecular weight (e.g., 10,000) polymers due to the high chain transfer characteristics of these solvents. By proper adjustment of the initiator levels and monomer concentrations water miscible solvents, either alone or in combination with water, could be used to prepare the hydrophobically functionalized cationic polymers of this invention. Thus, polymers produced by these teachings are effective viscosifiers for aqueous fluids and can be used for treating oily water. However, further improvements in polymer performance can be realized by using polymerization processes not containing chain transfer agents.
Two techniques have been found most useful for preparing hydrophobically associating copolymers of acrylamide and alkylacrylamide. The first method was based on the use of a water continuous microemulsion to disperse the oil soluble monomer in a solution of the water soluble monomers. Details of the procedures and techniques are taught by Turner, et al. in U.S. Pat. No. 4,521,580. A second method for preparing copolymers of acrylamide and alkylacrylamide was based on dispersing the oil soluble monomers using an aqueous micellar solution of the water soluble monomers. Suitable surfactants and the details of the polymerization are taught by Turner, et al. in U.S. Pat. No. 4,528,348. While either the microemulsion or micellar polymerization techniques can be used to prepare hydrophobically associating polymers containing a variety of water soluble nonionic monomers, a problem arises when the monomers have a strong interaction with the surfactants used in the polymerization. In particular, strong ionic interactions or complexes can be formed between cationic water soluble monomers, such as ethylenically unsaturated amine based monomers and anionic surfactants, such as alkyl sulfates and sulfonates. Thus, a new process is needed to overcome the limitations in these prior art processes. A copending application, Attorney Docket No. C-1960, teaches means of overcoming these deficiencies to enable preparation of the novel hydrophobically associating cationic polymer compositions of this invention.